Resistance-heated electric furnace



A g- 25, 1964 H. J. M. JERU RESISTANCE-HEATED ELECTRIC FURNACE 3 Sheets-Sheet 1 Filed Oct. 16. 1961 FIG.2

FIGS

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AEMe/ J54 Mar/z ate 0 United States Patent 3,146,337 RESISTANCE-HEATED ELECTRIC FURNACE Henri Jean Marie J eru, 4 Ave. du Chevalier Borda, Le Trait, France Filed Oct. 16, 1961, Ser. No. 145,101 Ciaims priority, application France Oct. 27, 1960 8 Claims. (Cl. 219-399) My invention has for its object to provide electric stoves or kilns in which the heating resistances are constituted by. thin metal strips forming at least a fraction of the inner walls of said stoves or kilns, said metal strips serving also as a support for an outer insulating lining. Such stoves or kilns are of particular interest since they are provided with a very low thermal inertia and consequently their starting is a very rapid .and speedy operation; furthermore their costs, both of construction and of operation, are considerably lower than those of other types of stoves. The stoves and kilns of this type are adapted to produce infra-red rays throughout their surface without the wave lengths at any point being too short. The heating strips may be blackened over their surface facing the-inside of the oven and brilliant on the surface facing the insulating strips. Lastly in such kilns and ovens, hot air is recycled and distributed in a very uniform manner between the different heating strips so asto produce a perfectly uniform temperature.

7 My invention has as its object the improvement of such furnaces and in particular it refers to improvements in the fitting ofthe metal strips so as to allow them to carrythe insulation without any deformation, to expand thermally without any risk of a short-circuihand to provide passage between them of a flow of recycled air.

My improved furnace is characterized by the fact that the heating strips are carried by a framework through the agency of ties engaging either insulating staples fitted between two adjacent metallic strips or else carrier rollers arranged transversely of the strips inside the oven. Said ties may be associated with metal springs adapted to compensate for anypossiblethermal expansion."

The arrangement of ties engaging directly the insulating staples or rollers allows the metal strips to carry the insulation while remaining very thin and thus providing a high electric resistance. Deformation of the convexity of the strips between the lines of rollers is prevented by stretching said strip longitudinally under the action of their own weight and of that of the insulation carried by them. Their inner surface, and in certain cases also their outer surface, runs over the rollers which may be constituted :by soapstone tubes. Thus, the volume of the oven does not increase upon increase in temperature.

With the arrangement of the spring-urged ties, the metal strips may be stretched independently of their weight in various directions. In particular when the metal strips expand under the action of heat, the springs hold the vault and the walls in their stretched condition, which prevents them from assuming between their carrier members, deformations which make them bulge inwardly of the stove, since such deformation would reduce their mechanical resistance and lead to the risk of short-circuiting. In such an arrangement provided with spring-urged ties, the volume of the oven increases slightly when heated.

Obviously, it is possible to combine the above-disclosed arrangement and in particular certain sections of the heating strips may be carried by springs while others move over rollers when they expand. A number of ties provided with rollers may also be associated with springs.

My invention will be better understood upon reading of the following description disclosing by way of example a preferred embodiment thereof, reference being made to the accompanying drawings wherein:

FIG. 1 is a cross-sectional view of my improved oven,

FIG. 2 is a longitudinal sectional view of the same oven,

FIG. 3 is a cross-section of a kiln according to my invention, 7

FIGS. 4 and 5 are sectional views, on a larger scale, of the ties carrying the metal heating strips,

FIGS. 6a and 6b are a side view and a view from i above of the blades holding the insulating material in position,

FIG. 7 is a diagrammatic perspective view of a further embodiment of my improved oven,

FIGS. 8, 9 and 10 show three further modifications of the means for suspending the heating strips.

The oven illustrated in FIGS. 1 and 2 includes parallel metal heating strips 1 arranged transversely of the oven, so as to form the vault 2 and the side walls 3 and 4 of said oven.

Said metal strips 1 are electrically interconnected in accordance with any desired Wiring diagram and they are fed by an ordinary transformer.

The strips 1 are suspended through the agency of ties or brackets 6, extending perpendicularly to the surface of the strips 1 and the outer ends of which are suspended from a framework 7. In alignment with a number of said ties 6, there are provided springs 8 adapted to make up for any heat expansion. At the inner ends of the ties and of the brackets, there are secured a number of aligned roller systems constituted by soapstone tubes 13 over which the heating strips are adapted to slide when they expand.

The medial section of each heating strip forming the upper generating line of the oven is secured as illustrated in FIG. 9 to a sheath 17 through which the air is recycled through insulating nozzles 18, said nozzles being secured on the one hand to said sheath, while on the other hand, they hold in position the strips 1 which assume a flaring shape underneath them.

The thermal insulation 9 of the oven is carried by the heating strips 1 and is constituted advantageously by a cushion of comminuted refractory bricks which is possibly covered by co-mminuted rock outside the stove.

In the preferred embodiment illustrated in FIGS. 2 and 4 it is apparent that the ties 6 carry the strips 1 through the agency of members It) of stainless steel each in the shape of an inverted T, of which the lateral arms 11 and i2 engage longitudinally corresponding insulating tubes 13 acting as rollers, whereas the central section 14 of the member 10 passes between said successive strips 1, with the interposition of insulating washers l5 and 16. As shown in FIG. 2, each insulating tube 13 extends throughout the breadth of a strip 1 and carries at its opposite ends an arm of a T-shaped member such as 10. It will be remarked that springs 8 act through compression on the ties 6.

In the embodiment illustrated in FIG. 3, the kiln 3th is constituted so as to show a semi-circular cross-section, the vault being carried by ties 32 associated with compensating springs 33 and suspended to longitudinal girders 34 bearing on arcuate cross-members 35.

Instead of producing insulating rollers as illustrated in FIG. 4, it is also possible to provide a simpler embodiment illustrated in FIG. 5 wherein the T-shaped member 50 is made of insulating material and carries directly the heating strips 1.

In the embodiment illustrated in FIG. 7, a furnace is constituted by blades or strips 70 folded side by side so as to form the side walls of a parallelopipedon whereas insulating carrier bars '71 engage the corners of said parallelopipedon and are engaged at each of their opposite ends 72 and 73 by corresponding ties '74; the upper ties 74 incorporate springs 75 adapted to compensate for thermal expansion.

FIG. 8 is a cross-section of a modified suspension for the heating strips 1 carrying the insulation 9, through the agency of ties'Sti and of'a compression spring 81 acting on v a a lower insulating plate 82 carrying the strips. The tie 80 is secured to a framework tube 83 through the agency of a welded metal strip 84.

FIG. 9 illustrates a modification in the suspension of the strips 1 by means of ties 90 with the interposition of the nozzles 18 communicating with the air recycling sheath 17.

FIG. shows how the strips 1 can be suspended through the agency of insulating rollers 100 over which is fitted a soapstone ring 101 held in position by a steel wire 102 forming the lower end of a tie.

In order to hold the insulation 9 in position, I may resort to metal strips 60 (FIGS. 6a and 6b) bearing against the outer surface of said insulation 9 and subjected to the tensioning action of the springs 62. Said metal strips 60 are provided with points 61 engaging the insulation and preventing the latter from sliding. It is also possible to resort to compression springs engaging the outer surface of the insulation.

What I claim is:

1. An electric resistance furnace with circulation of hot air by recycling, comprising an outer framework, a heating chamber substantially constituted by transversely extending thin flat metal strips which form electric heating resistances, said strips extending over the top and at least a portion of the sides of said heating chamber and being arranged in succession along the length of the furnace with spaces between them, suspension means supporting said strips and fixed to said framework, a lining of thermal insulation carried directly on and supported by said strips and surrounding the heating chamber, a hot air duct disposed longitudinally in the center of the upper portion of said heating chamber with nozzles disposed along its length for delivering hot air into the heating chamber in a downward direction, and means for removing hot air from the lower portion of the heating chamber and for recycling said removed hot air to said duct.

2. An electric resistance furnace with circulation of hot air by recycling as claimed in claim 1, in which said suspension means for the metal strips are elastic and include rods fixed to the framework by springs and the opposite extremities of which carry rollers which are of electrically-insulating material at least adjacent their extremities, said rollers passing below the adjacent metal strips, the portions of said rods extending through the spaces formed between adjacent strips being surrounded with electrically-insulating sleeves.

3. An electric resistance furnace with circulation of hot air by recycling as claimed in claim 1, in which said suspension means for the metal strips are rods fixed to the framework and the opposite extremities of which are provided with T-shaped parts of electrically-insulating material passing under two adjacent metal strips,

said T-shaped parts extending through the spaces between adjacent metal strips.

4. An electric resistance furnace comprising an outer framework, a heating chamber constituted by thin flat metal strips which form electric heating resistances, said strips extending transversely of the length of the furnace and being arranged in succession along the length of the furnace with spaces between them, suspension means supporting said strips and fixed to said framework, and a lining of thermal insulation carried directly on and supported by said strips and surrounding the heating chamber, said suspension means extending from the framework through the insulation and through the spaces between the strips and passing under the two adjacent strips.

5. An electric resistance furnace as claimed in claim 4, in which said suspension means for the metal strips are elastic and include rods fixed to the framework by springs.

6. An electric resistance furnace as claimed in claim 4, in which said suspension means include rollers of electrically-insulating material at least adjacent their extremities, said rollers passing below the adjacent metal strips.

7. An electric resistance furnace as claimed in claim 4, the portions of said suspension means that pass through said spaces formed between adjacent strips being surrounded with electrically-insulating sleeves.

8. An electric resistance furnace as claimed in claim 4, said suspension means including rods fixed to the framework and the opposite extremities of which are provided with T-shaped parts of electrically-insulating material passing under the two adjacent metal strips.

References Cited in the file of this patent UNITED STATES PATENTS Naylor Oct. 13, 1959 

1. AN ELECTRIC RESISTANCE FURNACE WITH CIRCULATION OF HOT AIR BY RECYCLING, COMPRISING AN OUTER FRAMEWORK, A HEATING CHAMBER SUBSTANTIALLY CONSTITUTED BY TRANSVERSELY EXTENDING THIN FLAT METAL STRIPS WHICH FORM ELECTRIC HEATING RESISTANCES, SAID STRIPS EXTENDING OVER THE TOP AND AT LEAST A PORTION OF THE SIDES OF SAID HEATING CHAMBER AND BEING ARRANGED IN SUCCESSION ALONG THE LENGTH OF THE FURNACE WITH SPACES BETWEEN THEM, SUSPENSION MEANS SUPPORTING SAID STRIPS AND FIXED TO SAID FRAMEWORK, A LINING OF THERMAL INSULATION CARRIED DIRECTLY ON AND SUPPORTED BY SAID STRIPS AND SURROUNDING THE HEATING CHAMBER, A HOT AIR DUCT DISPOSED LONGITUDINALLY IN THE CENTER OF THE UPPER PORTION OF SAID HEATING CHAMBER WITH NOZZLES DISPOSED ALONG ITS LENGTH FOR DELIVERING HOT AIR INTO THE HEATING CHAMBER IN A DOWNWARD DIRECTION, AND MEANS FOR REMOVING HOT AIR FROM THE LOWER PORTION OF THE HEATING CHAMBER AND FOR RECYCLING SAID REMOVED HOT AIR TO SAID DUCT. 